In recent years the coatings industry has become increasingly interested in high solids coatings. That is, coatings which can be applied by conventional techniques such as spraying, dipping, roll coating, etc., without the use of much volatile solvents or dispersants. The use of high solids coatings presents several advantages, including high film build per application, economy of materials since normally the solvents are lost to the ambient surroundings, and the diminuation of environmental control problems such as treatment of plant effluents to capture or destroy volatile pollutants.
However, to be a viable coating material, the high solids coating after application must produce under conventional curing conditions a film having, depending on the case, at least several of those characteristics required of coatings such as adhesion, flexibility, hardness, stain resistance, detergent resistance, solvent resistance, humidity resistance, and the like.
It should be noted that most high solids coatings are not true 100 percent solids coatings since in most cases minor amounts of organic volatiles are emitted on curing.
Although the prior art does disclose the use of polyester resins having reasonably high solids content, such compositions do not have the advantages of the low molecular weight, low viscosity composition and water compatibility as the compositions employed herein. The compositions herein, because of their low viscosity and low molecular weight, are easy to blend, mix and apply.
French Pat. No. 2,023,326 is directed to linear polyester coating agents having a molecular weight up to 3000 and U.S. Pat. No. 3,553,284 is directed to compositions comprising an aminoplast and a polyester of hexahydroterephthalic acid and a diol having adjacent hydroxy groups, e.g., ethylene glycol butanediol-(2,3) or cyclohexanediol-(1,2), such compositions are specific to hexahydroterephthalic acid and provide for compositions which have a substantial high viscosity and low water compatibility. German Pat. No. 2,019,282 teaches an aliphatic polyol, a mixture of aliphatic diols (and if necessary, cycloaliphatic diols) such as ethylene glycol and propane diol and one or more aromatic or cycloaliphatic dicarboxylic acids and one or more saturated aliphatic dicarboxylic acids along with an aminoplast resin. In contrast with the invention herein, this German patent teaches the use of a mixture of specific aliphatic polyol and the necessity for the employment of an aromatic or cycloaliphatic dicarboxylic acid.
Thus, it is surprising that the compositions herein will provide for useful coating when the art is devoid of any teachings which would lead one to believe that useful high solid coating compositions could readily be formulated from a simple ester-containing polyol and an amine-aldehyde crosslinking agent. In the past, ester-containing polyols were generally employed as starting materials for making resins.